Gastrointestinal regulatory peptides modulate mouse lymphocyte functions under serum-free conditions in vitro

Conditions are described for performing mitogen (Concanavalin A, Con A; lipopolysaccharide, LPS) and mixed lymphocyte reaction (MLR) cultures using serum-free medium. The effects of exogenously adding several gastrointestinal regulatory peptides (beta-endorphin, substance P, met-enkephalin, vasoactive intestinal peptide, bombesin and somatostatin) on the incorporation of 3H-methyl-thymidine was determined. It was observed that mitogen stimulation of lymph node cells with Con A was inhibited (70% of control) by vasoactive intestinal peptide (VIP) but spleen cells stimulated by LPS were insensitive to immunomodulation (98% of control). The ability of VIP to inhibit Con A induced thymidine incorporation was concentration dependent (10(-6) to 10(-18) M) and was not attributable to kinetic shifts or cell toxicity. None of the other tested neuropeptides affected Con A or LPS induced blastogenesis. MLR cultures were inhibited by VIP, beta-endorphin and somatostatin in a biphasic manner with maximal inhibition observed at 10(-8) to 10(-12) M. Both substance P and bombesin exhibited slight immunoenhancing properties at 10(-14) to 10(-18) M. Met-enkephalin was ineffective as an immunomodulator of MLR cultures. The utility of using serum-free medium in identifying neuropeptides with immunomodulatory properties are discussed.